My master’s thesis documents how the majority of reformers (and the confessions they wrote) include explicit affirmations of the Apostles’ Creed, the Nicene Creed, and the Athanasian Creed. In his book, On the Thirty Nine Articles (Paternoster Press, 1986) Oliver O’Donovan explains the motivations behind these affirmations of the catholic (universal) creeds. Although he writes about the English Reformers and the 39 Articles, his point holds true for the majority of Reformers and Protestant confessions:
“Nevertheless, it is clear what the Reformers wished to establish by their selection of documents: points of contact with the pre-Nicene church, with the Niceno-Constantinopolitan settlement of the trinitarian question, and with the Chalcedonian settlement of the Christological question (to which the Athanasian creed gave the most convenient documentary access). And in establishing these contacts with the church of the first five centuries they intend to be free of the opinions of any individual theologian, however great, and associate themselves only with the most considered doctrinal confessions of the church speaking as a whole,” (54).
In other words, the English Reformers did not want to be “Augustinians”, “Lutherans”, or “Calvinists,” in the sense of following the teachings of any one man. Rather, they affirmed the wise consensus of the church throughout history. They weren’t starting a brand new church; they were reforming something already there.